fix libguestfs mount order when inspecting

variable `mounts` sorted value is
[
    ('/boot', '/dev/vda1'),
    ('/', '/dev/vda2'),
    ('/var', '/dev/vda5'),
    ('/home', '/dev/vda6'),
    ('/home/q', '/dev/vda7')
]
but `/boot` directory is in `/` partition.

Fixes: Bug #1210371
Change-Id: I3d9cd59237bc4fc277415104c9170d2e372a1c25

nova/tests/fakeguestfs.py

@@ -25,6 +25,7 @@ class GuestFS(object):
         self.files = {}
         self.auginit = False
         self.attach_method = 'libvirt'
+        self.root_mounted = False
 
     def launch(self):
         self.running = True
@@ -50,10 +51,17 @@ class GuestFS(object):
         return ["/dev/guestvgf/lv_root"]
 
     def inspect_get_mountpoints(self, dev):
-        return [["/", "/dev/mapper/guestvgf-lv_root"],
+        return [["/home", "/dev/mapper/guestvgf-lv_home"],
+                ["/", "/dev/mapper/guestvgf-lv_root"],
                 ["/boot", "/dev/vda1"]]
 
     def mount_options(self, options, device, mntpoint):
+        if mntpoint == "/":
+            self.root_mounted = True
+        else:
+            if not self.root_mounted:
+                raise RuntimeError(
+                    "mount: %s: No such file or directory" % mntpoint)
         self.mounts.append((options, device, mntpoint))
 
     def mkdir_p(self, path):

nova/tests/virt/test_virt_disk_vfs_guestfs.py

@@ -37,12 +37,15 @@ class VirtDiskVFSGuestFSTest(test.TestCase):
         vfs.setup()
 
         self.assertEqual(vfs.handle.running, True)
-        self.assertEqual(len(vfs.handle.mounts), 2)
+        self.assertEqual(len(vfs.handle.mounts), 3)
         self.assertEqual(vfs.handle.mounts[0][1],
                          "/dev/mapper/guestvgf-lv_root")
         self.assertEqual(vfs.handle.mounts[1][1], "/dev/vda1")
+        self.assertEqual(vfs.handle.mounts[2][1],
+                         "/dev/mapper/guestvgf-lv_home")
         self.assertEqual(vfs.handle.mounts[0][2], "/")
         self.assertEqual(vfs.handle.mounts[1][2], "/boot")
+        self.assertEqual(vfs.handle.mounts[2][2], "/home")
 
         handle = vfs.handle
         vfs.teardown()

nova/virt/disk/vfs/guestfs.py

@@ -86,11 +86,25 @@ class VFSGuestFS(vfs.VFS):
                 _("No mount points found in %(root)s of %(imgfile)s") %
                 {'root': root, 'imgfile': self.imgfile})
 
-        mounts.sort(key=lambda mount: mount[1])
+        # the root directory must be mounted first
+        mounts.sort(key=lambda mount: mount[0])
+
+        root_mounted = False
         for mount in mounts:
             LOG.debug(_("Mounting %(dev)s at %(dir)s") %
                       {'dev': mount[1], 'dir': mount[0]})
-            self.handle.mount_options("", mount[1], mount[0])
+            try:
+                self.handle.mount_options("", mount[1], mount[0])
+                root_mounted = True
+            except RuntimeError as e:
+                msg = _("Error mounting %(device)s to %(dir)s in image"
+                        " %(imgfile)s with libguestfs (%(e)s)") % \
+                      {'imgfile': self.imgfile, 'device': mount[1],
+                       'dir': mount[0], 'e': e}
+                if root_mounted:
+                    LOG.debug(msg)
+                else:
+                    raise exception.NovaException(msg)
 
     def setup(self):
         LOG.debug(_("Setting up appliance for %(imgfile)s %(imgfmt)s") %